Heading into the NBA playoffs, it was clear that if Miami was expected to dominate through the Eastern postseason, top-seeded Oklahoma City was, at least, expected to survive and perhaps even thrive in the West, setting up a rematch of last year’s NBA Finals. In taking their first two games against the Houston Rockets, the Thunder were on track to do just that.

In a statement, Thunder GM Sam Presti said, “Our players’ health is our first and foremost concern. The Thunder’s medical team and several specialists we consulted with determined that Russell undergo a procedure to address the issue. We have thoroughly discussed this with Russell. Despite being the competitor and teammate that he is, he respects and understands the decision and is committed to come back even stronger.”

Between now and then, though, things figure to get rough for Oklahoma City. Coming into the playoffs, the Thunder actually rated higher than Miami on what’s known as the “Simple Ratings Scale,” which a metric that takes into account a team's margin of victory and strength of schedule. (Zero is the league average.) The Thunder finished the year at 9.15; Miami was at 7.03. The top challenger in the West, the Spurs, ranked third at 6.67, and the Clippers were at 6.43.

Based on pure statistics, then, the argument could be made that Thunder should even have been favored to beat Miami in the Finals. Take away the team’s No. 2 scorer—Westbrook averaged 23.3 points, six in the league—and it becomes much tougher to see how Oklahoma City can even reach the conference finals. In the second round, they’ll face one of two very difficult teams, the Grizzlies or Clippers, with LA leading that first-round series, 2-1.

There’s virtually no way to tell what the Thunder will look like now without Westbrook in the lineup—it’s just something we have not seen, not since he was backing up Earl Watson as a rookie in 2009. He took over the starting job that year, and never looked back. He had been the team’s starter for the last 377 games and 45 regular-season games. He has always been a workhorse, averaging 34.3 minutes per game, and in doing so, leaving precious little time for his backups.

Now it will fall to relatively untested Reggie Jackson to fill in for Westbrook, with 38-year-old Derek Fisher behind him. Jackson showed some signs of improvement over the course of the season, and played well in the first two playoff games including nine points and four assists in Oklahoma’s blowout win in the opener. It’s possible that the Thunder will be able to weather Westbrook’s absence and that he will return to action in a couple of weeks.

But Westbrook is an All-NBA type player and to truly replace him, the Thunder will need to tailor their offense even more heavily around their other All-NBAer, Kevin Durant. Durant is capable of carrying a team, but just how far he can carry the Thunder without Westbrook is a question.

Past Houston? Probably. But past the Clippers-Grizz winner in the second round? That’s a much tougher proposition. And even should the Thunder get past that gauntlet, they’re likely to see the Spurs in the conference finals. If Westbrook is still out, Durant will need far more help to get past San Antonio than the rest of the roster can provide.

A week ago, the Western Conference was the Thunder’s to lose. Now, even for upstarts like L.A. and Memphis, it is there for the taking.